(1) Field of the Invention
This invention relates generally to a vibrating compressor, and more specifically to a vibrating compressor comprising an external iron core, a permanent magnet, an internal iron core, and an electromagnetic coil vibratably supported by a mechanical vibrating system in a magnetic gap between the two iron cores to drive a piston connected thereto; the permanent magnet being composed of a high residual (remanence) magnetic flux density magnet, as represented by an alnico magnet, and a high coercive force magnet, as represented by a ferrite magnet, and disposed separately.
(2) Description of the Prior Art
Heretofore, there are two types of vibrating compressors; one type using a ferrite magnet as the high coercive force magnet, as shown in FIG. 1, and another using an alnico magnet as the high residual magnetic flux density magnet, as shown in FIG. 2. First, the vibrating compressor using a ferrite magnet will be described, referring to FIG. 1. A ferrite magnet 200 as a permanent magnet is formed into a hollow cylindrical shape going to consider the magnetic characteristics thereof and the outside diameter of the vibrating compressor, and disposed along the annular side surface of a cup-shaped external iron core 300. The ferrite magnet 200 is magnetized in the through-thickness, or radial, direction. An internal iron core 400 is provided to form a magnetic path together with the external iron core 300. An annular magnetic gap 500 is formed in a space between a magnetic pole 400' formed on the internal iron core 400 in such a manner as to oppose to the inner circumferential surface of the ferrite magnet 200 and the inner surface of the ferrite magnet 200. In the annular magnetic gap 500, disposed is an electromagnetic coil 100 vibratably supported by a pair of opposing resonating springs 600 and 700 via a coil support 800. A piston 900 is constructed substantially integrally with the electromagnetic coil 100 via the coil support 800, and is driven by the electromagnetic coil 100 to reciprocate in the vertical direction. A cylinder block 130 having a compression cylinder 110 engaged with the piston 900 is fixedly fitted by means of cylinder fixing bolts 150 to the external iron core 300 via a distance case 140. In the vibrating compressor having such a construction, when an alternating current is fed to the electromagnetic coil 100 via a lead terminal 180 and a lead wire 180', the electromagnetic coil 100 is caused to vibrate in accordance with the frequency of the alternating current to drive the piston 900. The reciprocating motion of the piston 900 causes a refrigerant, such as R12 gas, to flow from an inlet port 160 into a housing 190 in the direction shown by dotted-line arrows. The refrigerant, passing through an inlet pipe 160', is further introduced into the compression cylinder 110. The refrigerant flowing in between an suction valve 1000 and a discharge valve 120 is compressed by the piston 900. The compressed refrigerant is discharged in the direction shown by solid-line arrows through an outlet pipe 170' and an outlet port 170 into a refrigerating system condenser (not shown). The suction or discharge of refrigerant in the compression cylinder 110 is effected as the suction valve 1000 and the discharge valve 120 alternately open and close in accordance with the reciprocating motion of the piston 900. In this type of vibrating compressor using a ferrite magnet, the compressor performance is substantially deteriorated by temperature rise because the magnetic characteristics of ferrite magnets are lowered by approx. 18% by a temperature rise of 100.degree. C. This is not favorable for use in applications where a temperature rise of approx. 100.degree. C. is expected. Furthermore, a temperature difference of this degree often exists between the startup period and the steady-state operation of the compressor. For this reason, an attempt to maintain the compressor performance during the steady-state operation could increase the stroke of the piston excessively at the startup period, increasing the danger of the piston colliding against the discharge valve 120.
Next, the vibrating compressor using an alnico magnet will be described, fererring to FIG. 2. In the figure, like numerals represent like parts having the same functions as those shown in FIG. 1. Description of such parts is therefore omitted, and only those having different constructions will be described. Whereas the permanent magnet in the vibrating compressor shown in FIG. 1 is a ferrite magnet 200, that shown in FIG. 2 is an alnico magnet 200. The alnico magnet 200 is disposed in between the inside flat surface of the cup-shaped external iron core 300 and the top surface of the internal iron core 400. The alnico magnet 200 is magnetized in the height, or axial, direction. This type of vibrating compressor using an alnico magnet has the following drawbacks. The alnico magnet generally tends to be readily demagnetized, when an excess current flows in the electromagnetic coil 100, because it has a low coercive force and its inflection points exist in the second quadrant of the B-H curve. In addition, it is expensive because of the high cobalt content.